The disclosed technology regards a method and system for removing sodium chloride from wastewater. The disclosed technology further regards a method and system for treating wastewater from hydraulic fracturing.
Industries like the oil and gas industry generate high volumes of wastewater containing suspended solids, oil, impurities as well as sodium chloride and calcium chloride. Many of these industries generate high volumes of wastewater, which they dispose of by deep well injection or through wastewater treatment facilities. The cost of wastewater disposal and treatment is significant, and may be the source of recent earthquakes and other environmental concerns.
Of particular note, present methods and systems that treat wastewater to remove suspended solids, oil and other impurities, often generate additional sodium chloride and calcium chloride in the treatment of the water (this pretreated water with sodium chloride and calcium chloride is often referred to as ‘salt brine’), and then remove sodium chloride from the water in the same step as clean water removal (by evaporation, distillation or otherwise). However, in doing so the sodium chloride may precipitate, which precipitate plugs the apparatus facilitating the removal of clean water, causing equipment damage and downtime for repair. Using the novel methods of the present technology, this problem is overcome by precipitating out the sodium chloride prior to moving the water into the concentrator system or other dewatering apparatus.
By means of the disclosed method and system, the sodium chloride is precipitated out of the salt brine and removed before the removal of clean water. The sodium chloride precipitate may be high purity sodium chloride (>98%), depending on the effectiveness of the pretreatment process applied, noting that any impurities that remain in the salt brine and a small amount of calcium chloride may precipitate with the sodium chloride or be present in the moist sodium chloride removed from the system and dried. The remaining calcium chloride in solution (after precipitation of the sodium chloride) may be captured for other uses, and/or dewatered and recycled through the methods and system of the disclosed technology. Clean water captured in the dewatering process may then be returned to the environment or used for other purposes. Because the remaining brine is substantially free of sodium chloride, the dewatering process may be easily controlled to avoid the plugging issues of the prior art.
Therefore, the disclosed methods and systems provide a less expensive means to pretreat and separate industrial wastewaters into various saleable or disposable products, including high purity sodium chloride crystals, liquid calcium chloride and clean water. Specifically, simpler and less expensive evaporators (e.g., plate and frame heat exchangers) or similar technology for dewatering the brine solution may be used by the systems and methods of the present technology because the sodium chloride has been precipitated out and removed from the brine before the dewatering process. It is also anticipated that by simplifying the removal of clean water from the salt brine, a multi-effect evaporator can be employed to decrease total system energy consumption costs.